• Preheat your oven to 180°C (350°F) and grease a 9x9-inch baking pan. (Note: Do not use parchment paper to line the pan, because you will keep the cake in this pan to soak and serve it.)

Make the cake base

• In a large bowl, whisk the eggs, sugar, vanilla extract, buttermilk, salt, and vegetable oil until combined.
• Whisk in the flour, baking powder, and baking soda until almost combined.
• In a separate small bowl, whisk the hot coffee (or hot water) with the cocoa powder until smooth. Pour this hot mixture into your batter and fold it in gently with a spatula just until combined. Try not to overmix.
• Pour the batter into your prepared pan and bake at 180°C (350°F) for 30–40 minutes. A toothpick inserted into the center should come out clean.
• Let the cake cool in the pan for about 20 minutes so it is warm, but not boiling hot. Use a fork or a wooden skewer to poke holes all over the top of the cake.

Soak the cake

• In a medium bowl, whisk together the sweetened condensed milk, whole milk, and evaporated milk. To prevent lumps, mix your cocoa powder with a tablespoon of warm milk first, then whisk it into the rest of the liquid.
• Slowly pour the chocolate milk mixture over the warm cake. Put the cake in the fridge for at least 30 to 60 minutes to let the liquid soak in and allow the cake to cool completely before you frost it.

Make the chocolate whipped cream

• In a cold mixing bowl, combine the cold heavy cream, sifted cocoa powder, powdered sugar, and vanilla. Beat with an electric hand mixer on medium-high speed until stiff peaks form.
• Spread the whipped cream evenly over the cold cake. Garnish with some chocolate shavings or a little cocoa powder, then slice and serve directly from the pan.